1. Field of the Invention
The present invention relates to a superheavy oil emulsion fuel.
Further, the present invention relates to a method for regenerating a deteriorated oil-in-water (hereinafter abbreviated to O/W) superheavy oil emulsion fuel.
2. Description of the Related Art
Oil sand, bitumens (e.g. Orinoco tar and Athabasca bitumen), and so forth have attracted special attention as fossil fuel resources which do not fall under the category of petroleum, coal and LNG by virtue of their high reserve. Among the fossil fuel resources under the category of petroleum as well, asphalt obtained by removing the distillates, such as naphtha, from petroleum or residues obtained by heat-treating the asphalt are in surplus. These superheavy oils are usually an oleaginous material containing about 60 to 70% or, in some cases, 70% or more of a heavy fraction having a boiling point of 420.degree. to 450.degree. C. or, in some cases, 450.degree. C. or above, which is a vacuum distillation residue, and, as such, do not flow or have a viscosity as high as tens of thousands of centipoises or more. For this reason, if the use thereof as a fuel is intended without heating them to a temperature as high as 280.degree. to 300.degree. C., there occur not only problems in handling, atomization, etc., but also troubles of clogging of piping, etc., which renders them very difficult to use.
In recent years, an attempt has been made tog bring the viscosity of the superheavy oils difficult to handle close to that of water through emulsification of the superheavy oil in water. Namely, a proposal has hitherto been made with respect to an oil-in-water type (O/W type) emulsion fuel of a superheavy oil produced by emulsifying a superheavy oil (O) in water (W) with the use of a surfactant [see, for example, U.S. Pat. Nos. 5,024,676 (Assignees; Kao Corp. and Mitsubishi Jukogyo kabushiki Kaisha, Published on Jun. 18, 1991) and 4,923,483 (Assignee; Intevep, S. A., Published on May 8, 1990), and Japanese Patent Publication-A Nos. 313592/1989 (Published on Dec. 19, 1989) and 97788/1991 (Published on Apr. 23, 1991)]. The emulsion fuel has a viscosity relatively close to that of water and can sufficiently be atomized in a temperature range from ordinary temperature to 90.degree. C., and therefore is a fuel having a very good handleability. In the O/W type emulsion fuel, the lower the content of W (water), that is, the higher the content of O (oil), the better the quality of the fuel and the lower the fuel loss.
In order to handle the emulsion fuel in the same manner as that of conventional liquid fuel oils, it is necessary that the emulsion fuel has long-term stability, sufficient to withstand transportation and storage, and it is known that a surfactant plays an important role in maintaining the emulsion fuel emulsified in water in a stable state for a long period of time. However, in emulsion fuel produced by emulsifying a superheavy oil which has a very high heavy-fraction content, and which does not flow or has a viscosity as high as tens of thousands of centipoises or more, a further improvement in the long-term stability has been desired in the art.
In addition, to use the emulsion fuel effectively, regeneration of a deteriorated superheavy oil emulsion fuel may also be advantageous (see, for example, G.B. Patent No. 2220673, Published on Jan. 2nd, 1992). An emulsion system is a thermodynamically unstable one which breaks down with a lapse of time. In the above-described superheavy emulsion fuel as well, the emulsion partly breaks, i.e., deteriorates, during storage over a long period of time, including transportation by ship. When this deteriorated emulsion is burned as such, an unfavorable phenomena in the combustion, such as a high unburned content, frequently occurs. Further, the progress of the deterioration lowers the fluidity of the emulsion which increases the viscosity to such an extent that the emulsion cannot be handled as a fluid liquid, which renders the pumping thereof difficult. Therefore, what is important is to modify the deteriorated superheavy oil emulsion fuel into a fuel having a good fluidity and a low unburned content, i.e., to regenerate the deteriorated superheavy oil emulsion fuel prior to combustion.